The club confirmed the deal had been finalised, with the Belgium international signing a five-year deal with his new employers:
According to Paul Joyce of the Times, United will pay an initial fee of £75 million for the striker, as well as add-ons.
After leaving Everton, Lukaku posted the following message to the club's supporters on Instagram:
The move brings an end to Lukaku's four-year spell with the Toffees, having signed from Chelsea in the summer of 2014 for £28 million following a season on loan at Goodison Park. During his time on Merseyside, the former Anderlecht man emerged as one of the best young forwards in the game.
Hitting the back of the net is the biggest asset the striker will bring to his new side. While Lukaku doesn't have particularly sharp predatory instincts, he has a powerful left foot and is a dynamic runner with the ball at his feet.
His frame, physique and speed means he scores an array of different goals; once Lukaku is surging into space, he's almost impossible to halt.
He's going to improve, too. Although Lukaku has been a regular in the Premier League for a while, he's still only 24 years old. Football365's Daniel Storey noted how impressive the striker's scoring rate was for a player who is still developing:
Manager Jose Mourinho will be tasked with smoothing down the rough edges in his game, although there's no denying his potency in front of goal. His haul of 26 goals in 2016-17 for the Toffees is a testament to his finishing ability.
That ability is what the Red Devils need most, having found the back of the net just 54 times last season and being held to 15 Premier League draws.
Lukaku has thus far proved he can be a prolific goalscorer in the Premier League both for the Toffees and West Bromwich Albion. With the kind of service he can expect at Old Trafford from the likes of Paul Pogba, Henrikh Mkhitaryan and Juan Mata, he should be able to thrive at United.